Aerotech L2300G Experiences

[CCotner]

I keep hearing people have bad experiences with this motor, and it's scary, since we have 14 of them to start flying starting this weekend for a research project. We are grain bonding them as suggested by Aerotech directly. What issues have people had/what were the resolutions?

Recently one blistered a case-we think this was because of the huge, thick, full-width long-burning delay grain, so we're thinking about inhibiting both ends of the delay grain (one is already epoxied over), and/or making a bunch of plastic plugs and saving the delay grains for a fun bonfire. But surely this can't be a common problem, or how would it have become certified? What's up with that?

 

[patelldp]

I keep hearing people have bad experiences with this motor, and it's scary, since we have 14 of them to start flying starting this weekend for a research project. We are grain bonding them as suggested by Aerotech directly. What issues have people had/what were the resolutions?

Recently one blistered a case-we think this was because of the huge, thick, full-width long-burning delay grain, so we're thinking about inhibiting both ends of the delay grain (one is already epoxied over), and/or making a bunch of plastic plugs and saving the delay grains for a fun bonfire. But surely this can't be a common problem, or how would it have become certified? What's up with that?

Are you flying this at a NAR/TRA Commercial launch? If not, I might recommend modifying the motor a tad so that you remove the delay grain entirely.

Remove the smoke grain, trim the liner until the liner engages the step of the bulkhead sufficiently, insert bulkhead as you normally would, and then use a stack of nozzle washers on top of the bulkhead to make up the difference.

That's all fine and dandy, but the blistering (Assuming the resulting blister is a "bubble," which demonstrates there is a pressure component to the flaw) will not be prevented. It appears that there is an insulation problem with this motor, which could be the result of insufficient liner material, insufficient engagement of the bulkhead step, uneven liner cutting, etc.

 

[3stoogesrocketry]

Flown 2 , never had a problem with them . Not a huge fan of them though .

Eric

 

[n3tjm]

The blisters are caused by high pressure, high temp gas leaking around the seal ring during thrusting phase. This is a common problem with the RMS system, and is the reason why a lot of RMS hardware now uses the aluminum forward seal ring which sealed to the end of the liner with an o-ring. Not sure about that load, does it have a aluminum seal ring or a fiber seal ring? If it was a fiber ring, was it epoxied into the liner? I would not reuse a blistered case. The strength of the aluminum has been compromised.

 

[GRIFFIN]

The blisters are caused by high pressure, high temp gas leaking around the seal ring during thrusting phase. This is a common problem with the RMS system, and is the reason why a lot of RMS hardware now uses the aluminum forward seal ring which sealed to the end of the liner with an o-ring. Not sure about that load, does it have a aluminum seal ring or a fiber seal ring? If it was a fiber ring, was it epoxied into the liner? I would not reuse a blistered case. The strength of the aluminum has been compromised.

Uuuum...this motor uses AMW snap ring hardware.

 

[n3tjm]

Uuuum...this motor uses AMW snap ring hardware.

Oh my bad. I was thinking it was a 75mm RMS load. That's what I get for not checking the motor specs before I comment. My apologies.

Its quite possible that the tracking smoke blistered the case. I don't think AT use the extra thick casting tubes AMW did for the smoke grains.

 

[CarVac]

Oh my bad. I was thinking it was a 75mm RMS load. That's what I get for not checking the motor specs before I comment. My apologies.

Its quite possible that the tracking smoke blistered the case. I don't think AT use the extra thick casting tubes AMW did for the smoke grains.

Looking at our reloads, the smoke grain casting tubes are indeed not any thicker than the propellant casting tubes. That's an interesting insight and something that would be simple for AT to change.

Based on the short motor burn duration and the raw thickness of the smoke grain (it's ~1.3 inches long), I'd suspect that the smoke cooks the case for a long time. Disregarding the amount consumed during the burn, that thickness (if the same formula as normal AT delay grains) would burn for over 40 seconds!

That smoke duration, along with the full-width extent and lack of insulation, would certainly cook the case pretty hard.

 

[GRIFFIN]

Oh my bad. I was thinking it was a 75mm RMS load. That's what I get for not checking the motor specs before I comment. My apologies.

Its quite possible that the tracking smoke blistered the case. I don't think AT use the extra thick casting tubes AMW did for the smoke grains.

The smoke grain is the same looking as the Amw's. I will say, I agree with you about the smoke as the potential cause of the trouble

 

[CarVac]

Is there any reason motor manufacturers don't use 7075 aluminum instead of 6061 aside from cost? It is supposed to keep a LOT more strength after losing its temper than 6061; you could run longer-burning motors with thinner liners without worrying about structural integrity.

 

[dixontj93060]

I keep hearing people have bad experiences with this motor, and it's scary, since we have 14 of them to start flying starting this weekend for a research project. We are grain bonding them as suggested by Aerotech directly. What issues have people had/what were the resolutions?

I have fired one L2300G. Great flight, but unfortunately can give you no feedback as I lost the booster.

For added protection, why don't you just upgrade the liners? Loki has some on their specials page here: https://www.lokiresearch.com/specials.aspx

 

[ClayD]

Is there any reason motor manufacturers don't use 7075 aluminum instead of 6061 aside from cost? It is supposed to keep a LOT more strength after losing its temper than 6061; you could run longer-burning motors with thinner liners without worrying about structural integrity.

its a difference in failure mode....
I dont think its illegal to use in EX, but i believe 6061 is codified in NFPA as a standard for commercial motors.

 

[CCotner]

For all intents and purposes, we are going to commercial launches. So we are looking for solutions that don't make the motors experimental.

Are you flying this at a NAR/TRA Commercial launch? If not, I might recommend modifying the motor a tad so that you remove the delay grain entirely.

Remove the smoke grain, trim the liner until the liner engages the step of the bulkhead sufficiently, insert bulkhead as you normally would, and then use a stack of nozzle washers on top of the bulkhead to make up the difference.

That's all fine and dandy, but the blistering (Assuming the resulting blister is a "bubble," which demonstrates there is a pressure component to the flaw) will not be prevented. It appears that there is an insulation problem with this motor, which could be the result of insufficient liner material, insufficient engagement of the bulkhead step, uneven liner cutting, etc.

 

[patelldp]

For all intents and purposes, we are going to commercial launches. So we are looking for solutions that don't make the motors experimental.

Then load it and fly it, maybe cross your fingers.

That's about all you can do.

 

[CarVac]

Then load it and fly it, maybe cross your fingers.

That's about all you can do.

Based on the discussion, we can (and probably will) inhibit the smoke grain to keep it from roasting the case.

 

[JDcluster]

Buy better liners.....Those spiral wound can be hit or miss.
I've seen some ex guys pull out charcoal after use.
Convolute liner is the way to go but, AT is taking the cheaper road.


JD

 

[CCotner]

Better liners sounds like the kind of advice that we can implement, as well as bonding in and inhibiting the smoke grain. We can't buy better liners for this launch, but we will still have ten more flights after this weekend. Where/what should we buy, if that information isn't too sensitive for this public forum? Neither of us have done exp stuff before.

 

[CCotner]

One other thing we can and will do is fully document the motor assembly, flight, and aftermath; we want to be as armed as possible for warrantee claims afterward.

 

[GRIFFIN]

warrantee claims afterward.

Don't count on it.

 

[troj]

One other thing we can and will do is fully document the motor assembly, flight, and aftermath; we want to be as armed as possible for warrantee claims afterward.

If you don't use the liner they provide, I can all but guarantee they'll say "No". Likewise, if you're not following their instructions to the letter -- if you inhibit the smoke grain, and they didn't tell you to, for example, forget it.

-Kevin

 

[patelldp]

It's unlikely that Aerotech will replace your AMW or Kosdon hardware. If you CATO a Dr. Rocket, you will get a "replacement in kind" of an AT case, but they do not offer a "replacement in kind" for snap ring hardware.

Fly at your own risk.

 

[patelldp]

Warranty from the instructions:

NOTICE: As we cannot control the storage and use of our
products, once sold we cannot assume any responsibility for
product storage, transportation or usage. RCS and/or Kosdon
Enterprises shall not be held responsible for any personal injury
or property damage resulting from the handling, storage or use
of our product. The buyer assumes all risks and liabilities
therefrom and accepts and uses KBA/RCS products on these
conditions. No warranty either expressed or implied is made
regarding KBA/RCS products, except for replacement or repair,
at RCS's option, of those products which are proven to be
defective in manufacture within one year from the date of original
purchase. For repair or replacement under this warranty, please
contact RCS. Proof of purchase will be required. Note: Your
state may provide additional rights not covered by this warranty.

Contact Aerotech/RCS and ask for further information prior to flying these loads.

 

[daveyfire]

We have had a few guys in our club blister cases with the L2300. AT did not provide any warranty support for the hardware.

 

[patelldp]

We have had a few guys in our club blister cases with the L2300. AT did not provide any warranty support for the hardware.

I am assuming that they did not receive a new reload, either. In other words, they are damn near close to a Single Use motor with a recyclable nozzle and bulkhead.

 

[GRIFFIN]

The only way I would buy another one would be if they made it a "FU" motor. :wink:

 

[CarVac]

We have had a few guys in our club blister cases with the L2300. AT did not provide any warranty support for the hardware.

Where did they blister?

 

[JDcluster]

The smoke grain could very well be the problem.
That is why I hate using them. It makes clean up allot harder.



JD

 

[CCotner]

If you don't use the liner they provide, I can all but guarantee they'll say "No". Likewise, if you're not following their instructions to the letter -- if you inhibit the smoke grain, and they didn't tell you to, for example, forget it.

-Kevin

Just talked to Aerotech. Due to uncooperative behavior by Kosdon and AMW, they cannot replace damaged cases, and they seem pretty confident (naturally) that the reload isn't going to malfunction, the case will. What he suggested we do:

Inspect the liner, especially the ends, for any damage or softness
Fully Grease the liner
Grain-Bond with epoxy, using 1/32 orings between grains as spacers, being sure to not inhibit the ends of the grains
Inhibit the smoke-grain if we don't need it, with grease or epoxy
Bond-in the smoke grain as if it were a propellant grain
Don't muck around with the snap rings; don't scratch the case anodizing, make sure they are seated properly, etc.
The snap rings are not symmetrical-they have a rounded edge and a straight edge, the straight edges should be outward
make sure you use the nozzle washers properly
don't use an unnecessarily massive ignitor


They said that buying better liners wouldn't be necessary but couldn't hurt.

 

[daveyfire]

they seem pretty confident (naturally) that the reload isn't going to malfunction, the case will.

LOL - "it's not the thing that makes all the heat in the tube that causes the tube to get heat damaged, it's the tube's fault." Some logic.

All the cases that I have seen blister are blistered at the head end of the liner, just below the smoke grain. Having seen many an EXer accidentally cook their case with the smoke grain, that seems like the likely culprit.

 

[daveyfire]

I dug back through an e-mail chain from one of the flyers who had a problem with the L2300 in a brand new AMW case, and found this response from AT. At least they're being consistent with their claim that it's the tube's fault that the propellant is melting it, rather than the insulation's or the propellant's.

We would have warrantied the re-load had it had a failure, but the reload did not fail... What we don’t warranty is the case, again, as we do not manufacture the case we cannot guarantee its integrity, manufacturing quality, specs etc. This is a case failure, not a re-load failure and it is my guess that you have not gone to the manufacturer of the case to complain about the quality of the case, you just presume it is the load... these loads are certified and produced to fly in these motors, if they were not built for that purpose the certification would have been denied. We stand by our decision and would suggest that you consult with the manufacturer of the case to see if they will stand by their product. There are too many variables involved for us to warranty another manufacturers product.

 

[CarVac]

LOL - "it's not the thing that makes all the heat in the tube that causes the tube to get heat damaged, it's the tube's fault." Some logic.

All the cases that I have seen blister are blistered at the head end of the liner, just below the smoke grain. Having seen many an EXer accidentally cook their case with the smoke grain, that seems like the likely culprit.

I guess the way it goes is that the propellant eats up the liner, and then the smoke grain deals the finishing blow.
Is Aerotech's smoke grain slower and longer burning than other manufacturers'? I am pretty sure, for example, that CTI delay grains have a much higher regression rate, based on how much gets drilled out for a given reduction.

If this is the case, the same sized smoke grain would cook the liner and case for much longer than a different brand's.